The atmosphere of Titan is characterized by a complex
organization of chemical and physical processes that serve
to distribute Titan's varied collection of organic
compounds. Wilson and Atreya (2004) attempted to describe
this system through a photochemical model based on Voyager
and ISO observations along with ground-based observations.
Recent observations from the Cassini-Huygens mission has
further elucidated the nature of Titan's physicochemical
system, corroborating some of the predictions of Wilson and
Atreya (2004) such as lower levels of ethane condensation,
while raising many other questions. For instance, the
significant divergence of thermal profiles retrieved by the
UVIS, INMS, and HASI instruments has profound implications
in the interpretation of the density of the background
nitrogen atmosphere, the characterization of the diffusive
regime, which helps distribute minor constituents in the
upper atmosphere, and the importance of the chemical
schemes, which provide sources and sinks for said
constituents. Wilson (2005), taking the UVIS-retrieved
temperature profile, demonstrated reasonable agreement with
UVIS observations including CH4 and good agreement with INMS
observations with the exception of CH4, by assuming a medium
homopause level similar to that reported in Wilson and
Atreya (2004). However, adopting the INMS or the warmer HASI
temperature profiles gives different results. These recent
Cassini-Huygens observations will be interpreted in the
context of our photochemical model results in an effort to
understand the processes that govern Titan's constituents.

This research is supported by a grant from the NASA Outer
Planets Program.